Not applicable
The present invention relates to the test and measurement of video image signals, and more particularly to video picture quality assessment using spatial location with or without subsampling.
Both subjective and objective measurements of video quality degradation in video image signals have been done. In subjective measurements human subjects visually compare and rate the degradation between an original and an impaired video image signal. Objective quality measurements are done by comparing an impaired video image signal to its original video image signal. The comparison includes such processing as transforming video image signals into bit-map form, adjusting mutual amplitude gain, offset and spatial shift, filtering them in some fashion, subtracting them from each other, then filtering some more and representing the results either as error maps or as statistics derived from these maps.
Subjective measurement methods suffer from a lack of reproducibility and consistency. Objective methods are mechanistic and lack the ability to differentiate between areas where human observers pay attention (xe2x80x9cattentional factorsxe2x80x9d) and those areas without much interest to humans.
U.S. Pat. No. 5,940,124, filed Jul. 17, 1997 by Bozidar Janko and John Edwards entitled xe2x80x9cAttentional Maps in Objective Measurement of Video Quality Degradationxe2x80x9d, addresses content-based picture quality by describing a method of isolating a particular content element, such as a human face, and applying a greater quality weighting to such element. However this method requires either a manual input as to which elements in the picture should be weighted more or a special processing algorithm that makes such a determination for every picture.
It is well known that certain portions of a video picture are more likely to carry important information than others. The video industry uses a so-called xe2x80x9csafe picturexe2x80x9d and xe2x80x9csafe titlexe2x80x9d area inside which the important elements of a program are generally captured by a camera and in which titles are contained. Essentially the safe areas define the central portion of the screen, i.e., the periphery of the video image is outside the safe area. Also presently measurement of picture quality is a compute intensive operation that cannot be performed in real time. For certain applications, such as satellite transmission where it is desired to compress the various channels as much as possible without appreciable degradation so that the satellite may carry more channels, realtime processing is desireable.
What is desired is a simpler method of picture quality assessment using spatial location with or without subsampling rather than attentional maps.
Accordingly the present inventions provides picture quality assessment using spatial location with or without subsampling. A video sequence, either a reference or from a device under test, is divided into a plurality of arbitrarily sized, geometric segments. A segment weighting map is generated that provides a low threshold for xe2x80x9csafe picturexe2x80x9d segments of the video picture and a high threshold for other segments. Weighting coefficients may be used instead of thresholds. Optionally one or more of the segments may be subsampled to reduce the amount of processing required for realtime applications at the expense of measurement accuracy. The video picture, both reference and test, is captured, segmented, optionally subsampled and processed by an appropriate picture quality assessment algorithm, such as JND or PSNR for example, to generate a quality error value for each segment. The segment weighting map is applied to each segment, and the result is displayed as an error map.
The objects, advantages and other novel features of the present invention are apparent from the following detailed description when read in conjunction with the appended claims and attached drawing.